FOOLED YA! When It’s NOT a Roof Leak

January 9, 2019

Where there’s water, there must be a roof leak, right?

Unfortunately, it’s not quite that simple. A leak evaluation performed by roofing professionals sometimes reveals another culprit.

HVAC Systems

If the roof isn’t to blame, the most common source of water infiltration is HVAC units. Once the location of the leak is identified, a thorough investigation of the roof area is conducted.

Weather permitting, the roofing contractor will perform a water test, using a hose to douse the roof with water for 15-30 minutes. Someone inside will communicate via cell phone with the man on the roof if the leak is recreated. If there’s no evidence of water, the hose will be used to wet the flashing. Core cuts may be taken to check insulation for moisture.

If no roof defects are discovered, the next logical place to investigate is the HVAC equipment there. If the facility manager suspects that may be the problem, it’s beneficial to have the HVAC contractor onsite during the leak evaluation; this allows both parties to work together to investigate and solve the problem, rather than each pointing a finger at the other later.

Common causes of water are the pre-drilled holes where wires run down into the building from the unit, a blocked condensate line, and a failed gasket or weatherproof seal.

Winter Condensation

On an older roof, insulation may have shifted or shrunk, creating a gap between the exterior and interior wall. The heat loss from the building comes up through the flashing and with no insulation there (and cold outdoor temperatures), condensation occurs. Your roofing contractor may even be able to feel ice behind the roofing membrane or flashing.

As warm, humid air rises, the moisture it contains can also condense on the cold underside of the roof assembly. Without ventilation allowing the moisture to escape, water droplets form. Dripping water is most likely when outdoor temperatures hit their high for the day and the sun is out.

Frozen Water Line

When pipes freeze, expect water. Water lines in the ceiling can crack and cause everything from a steady flow of water to small, slow drips. Unfortunately, the tell-tale signs of a broken water supply line (blistering paint, water stains, mustiness, etc.) may be the same as a roof leak. When your roofing contractor comes to perform a leak evaluation, a thorough inspection and the inability to recreate the leak will help them determine the real source of the problem.

Block Wall

Flashing may only extend up a brick or block wall six to eight inches. If the masonry wasn’t sealed or waterproofed, it could be the source of your leak. These surfaces are porous, so they easily absorb moisture. While not truly a roofing problem, it’s possible for your roofer to encapsulate the entire block wall in membrane or coat it with an acrylic coating as a solution.

Cracks and mortar issues, possibly because the building has settled, also exacerbate the problem; tuckpointing repair is the best solution in this instance.

Windows & Doors

Heavy rain combined with strong winds can test even the best weatherproofing. Around doors and windows, seals can fail and let water in. Weep holes in window frames can become blocked, leaving water nowhere else to go, but to drain indoors. It’s easy to mistake water coming in around an upper-story window or roof access door, as a roof leak. Once the true cause is identified, your roofing contractor will refer you to another building professional for the repair.


When skylights become old, cracked, or brittle, water will infiltrate every time it rains or snows. You’ll have the same result when sealants and glaze fail. Your roofing contractor’s water test will reveal whether your skylight is the source of the water. If it is, you have two options: 1) replace it or 2) if the condition allows and it’s made of fiberglass, restore it with multiple coats of an acrylic coating made specifically for this purpose.

If you’re unsure of why you have water in the building, and you suspect it’s coming from the roof, contact your roofing contractor for a leak evaluation to be sure. An experienced roofing contractor has seen it all and will  investigate the cause so you can find the most appropriate remedy.

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